Assessing Anemia Secondary to Hemolysis in Hemodialysis Patients

Nephrology Nursing Journal, April, 2001 by Jamie Behrens

Assessment of Hemolysis

In cases of overt hemolysis, the diagnosis is self-evident. Occult hemolysis is more difficult to diagnose because there is not a visible change in the appearance of the blood, and laboratory assessment is required (Table 2). Several tests may be used to confirm the diagnosis, including: (a) haptoglobin, (b) plasma-free Hb (c) [sup.51]Cr-RBC survival time, (d) blood smear with a test for Heinz bodies, (e) Coomb's test for immunologic mediators, and (f) lactate dehydrogenase.

Table 2: Laboratory Findings in Hemolytic Anemia

Parameter           Findings in Hemolytic Anemia (Normal range)

RBC                 Decreased (Males; 4.6 to 6.2 x [10.sup.6] cells/
                              [mm.sup.3] Females: 4.2 to 5.4 x
                              [10.sup.6] cells/[mm.sup.3]

Hb                  Decreased (11 to 12 g/dL)

Hct                 Decreased (33% to 36%)

MCV                 Unchanged (Males: 80 to 96 fL
                               Females: 82 to 98 fL)

MCH                 Unchanged (27 to 33 pg/cell)

MCHC                Unchanged (31 to 35 g/dL)

Reticulocytes       Increased (0.5% to 2.5% of RBCs)

Antigoblin tests    Positive (Negative)
(in immune types)

Serum haptoglobin   Decreased (40 to 240 mg/dL)

Plasma free Hb      Increased (100 to 210 IU/L)

Heinz bodies        Present (Absent)

Haptoglobin (Hb-binding protein) is frequently used to screen for the hemolysis. This acute-phase protein binds Hb that is freed during intravascular hemolysis and transports it to the reticuloendothelial system. The absence of haptoglobin or a decrease to below the normal adult level of 40 to 240 mg/dL often indicates hemolysis. However, haptoglobin results must be interpreted with caution, since lower levels may also be seen in such conditions as folate deficiency, sickle cell anemia, thalassemia, hypersplenism, liver disease, estrogen therapy, or pregnancy. Also, patients who experience hemolysis during an infection or inflammation or during corticosteroid therapy may have normal or elevated haptoglobin levels because these conditions cause a confounding increase in haptoglobin. Further, nephrology clinicians should be aware that about 1% to 5% of African Americans have a genetic deficiency of haptoglobin--the test is inappropriate as a screening tool in patients with confirmed haptoglobin deficiency (Jordan, 1996; Wallach, 1996).

Plasma-free Hb measures the amount of Hb that is unattached to RBCs in the plasma. Normal values of less than 3 mg/dL are typically elevated in the presence of intravascular hemolysis (Jordan, 1996).

RBC survival time can be assessed by affixing RBCs to radioactive chromium 51 and measuring the half-life. This test has its greatest utility in evaluating unknown causes of anemia from blood loss, hemolysis, or removal of RBCs from the spleen. In dialysis patients who have hemolysis, RBC survival time is typically reduced (Fischbach, 1996). However, because RBC survival is highly variable, a baseline level is helpful to determine the trends in RBC survival.